Hydraulically damping mounts are used in engine vehicles to damp and to cancel occurring vibrations. The hydraulic functions can also be implemented in bushes, which results in fundamental design amendments, however, due to compressed constructions. In particular, such mounts are used as chassis mounts or engine mounts. The fluid-filled chambers are partially limited by elastomeric membranes. Their blowing rigidity significantly contributes to the overall rigidity of the mounts, the dynamic rigidity, in dynamic loading of the mounts.
Decoupling devices serve in mounts of the aforementioned type to lower the dynamic rigidity for high-frequency, low-amplitude excitations. In high-amplitude vibrations the decoupling member closes the inlet opening of the decoupling channels at the decoupling cage. Only then, a significant amount of fluid is pumped through the damping channel, thereby causing dampening of occurring vibrations.
DE 43 05 173 C2 discloses a hydraulically damping mount bush with hollow-cylindrical mount core and an outer sleeve. The mount core is supported by the mount spring of an elastomeric material. The space between the mount springs has two fluid-filled chambers separated by supporting studs. The chambers are connected with each another by a damping channel and a decoupling channel. The decoupling channel has a decoupling cage receiving a freely movable spherically shaped decoupling member.
EP O 304 349 A1 discloses an elastic joint comprising two fluid-filled chambers which are connected to each other by a first channel and a second channel. The second channel has spherically shaped closing means capable of moving in the second channel between two end points having reduced channel diameters and capable of closing the second channel if the closing means are closely fitted on one end point. Thereby, the diameter of the closing means is barely smaller than the diameter of the second channel.
DE 197 32 123 A1 discloses a sleeve-shaped hydraulically damping radial rubber mount with at least two hydraulic working compartments connected with each other via a throttle channel and via a bypass channel for damping shock amplitudes. A decoupling member comprised of a decoupling cage and an inserted elastomeric loose piece is introduced into the bypass channel. The elastomeric loose piece thereby bears at most loosely with all its side surfaces on the surrounding wall surfaces of the decoupling chamber. The resonance of the mount for low amplitudes can therefore be shifted to a frequency range around 200 Hz, while in the presented example, the mount has a resonance of around 40 Hz for high amplitudes.
However, the non-spherically shaped decoupling members of the known mounts are formed so that they can tilt or tip during operation. Thus, the operational safety and function of the mounts at low amplitudes is guaranteed only to a limited degree.
In addition, hydraulic simulations show that the resonance frequency in a hydraulically active channel is higher the less mass vibrates in the channel, i.e. the shorter the channel is relative to its cross section. For particularly good results, the cross section of the decoupling channel is to be maximized, and its length or vibrating mass is to be minimized. However, the minimal length of the decoupling channel is limited by the width of the supporting studs. Maximizing the cross sections of the decoupling channel is directly linked to the construction type of the mount bushing. Thus, the available construction space is defined by a portion of the guide cage which externally limits and fixes the supporting lug, and the outer pipe. Typically, the construction space has a very small height in radial direction. Thus, spherical decoupling members do not optimally utilize the mostly flat, longitudinal cross section between the outer sleeve and the cage.
Therefore, the object of the invention is to provide a hydraulically damping mount having a small dynamic rigidity at low amplitudes and an improved operational safety.
To solve this object, it is proposed in the mount of the previously mentioned type to form the decoupling device so that its inflow sides always face the fluid flows during a fluid-induced movement of the decoupling device.